lathe tool advice

[Gordon WParticipant @gordonw]

[Gordon WParticipant @gordonw]

Can some experienced person give advice on what material to use for what I call rough turning? Problem is most of my stuff is made from scrap of unknown quality. I am just trying to turn a disk in 3/8″ steel which I have hacked with angle grinder to near round. A HSS tool blunts very quickly, an insert tip breaks very quickly so forget them, a brazed carbide seems best, but any sort of intermittent cut soon cracks the edge. I can’t avoid int . cuts, any ideas please?

[CirclipParticipant @circlip]

You COULD quite easily start a carbide/HSS flame war with this one Gordon, BUT, HSS is sharpened using a conventional grinding wheel so you can have more stabs at the offending material without damaging Carbide tips or inserts.

 

  Problem with unknown materials is just that. As a newbie, (And to be asking this question doesn’t take rocket science to work out) you should restrict yourself to materials with known properties before commiting yourself to rubbish (In material terms). Once you’ve got how to sharpen tools to machine KNOWN properties, then you can deviate.

 

  Basically you’ve told us it’s Metal. Turning speed?? Coolant?? What colour are the chips coming off?? What SHAPE are the chips??

 

  I’m NOT mocking OR taking the ——- micky, but these are salient features.

 

 MOST Carbides don’t like intermittent cuts, but I’m not discounting them, It’s just that I preferr to do it properly and use HSS.

 

   Regards  Ian.

[mgjParticipant @mgj]

Probably you have a piece of toughened heat treated steel and its gong to be a bastard from start to finish.

 

HSS ground for tough materials will do it as Circlip suggests. or you get a proper tip designed for tough materials.  Angles for grinding the right sort of tool are in the ME handbook

 

You could try just heating it to red heat, holding it there for 10 minutes per inch, and then allow to air cool. Might soften it.

 

If it doesn’t I think I’d invest in a chunk of 220M07  and  enjoy my turning.

Edited By meyrick griffith-jones on 21/12/2009 18:05:45

[Ian S CParticipant @iansc]

How slow can you go?Some of the Chinese lathes don’t go below 120rpm,I find with some of the rubbish that I get I’v got to get into back gear and 60rpm is fast enough.I try to keep away from old half shafts etc,but some times can’t avoid flame cut stuff with hard edges,normally use carbide tips on that stuff and keep it hard at work so that it does’nt rub.Ian S C

[Don BrymerParticipant @donbrymer78910]

Gordon,

First question, can you file the material with a sharp flat smooth file? If yes, you will be able to turn the work with HSS. For the diameter mentioned try a starting spindle speed of around 150RPM or perhaps less, with cutting fluid or straight cutting oil applied with a small paint brush.

If no, then a carbide insert may be OK, but increase the spindle speed to 1500RPM or higher. Try to get the depth of cut under any surface irregularities. If the insert is constantly chipping you could be using a finishing grade insert or the spindle speed is far too slow.

I think that the HSS is the better option, but do not grind the tool rake angles too acute. Limit the angles to 8 to 10 degrees.

Regards,

Don.

[CirclipParticipant @circlip]

I keep re-reading the O/P but keep missing the diameter. Which line is it on??

 

   Regards  Ian.

[Les Jones 1Participant @lesjones1]

Hi Ian,

              I can see your frustration at not being able to get the information from Gordon

that is required to be able to help him. We had the same problem getting in information about a switch last week but the information was eventually  supplied.

Les.

[Eric CoxParticipant @ericcox50497]

Why use an angle grinder on something as small as 3/8″ Dia. The heat generated would have an adverse effect on the material. Next time use a file or cut a blank with a hacksaw 7/16″ or 1/2″ square and turn to round.

[KWILParticipant @kwil]

I seem to think it was 3/8″ thick.  If you cut it slightly oversize with the disk cutter then there will be material to turn without the intermittent cut that kills tools!

[CirclipParticipant @circlip]

That seems to be two of us that are “Thick” Kwil.

[Gordon WParticipant @gordonw]

thanks for the advice everybody. My fault didn’t give all relevent facts, this particular job is 5 1/2″ dia. x 3/8″ thick. I thought I’d cracked the job with a brazed tip, 90 deg. point with a 1mm rad. was cutting ok until back edge cracked off. Would love to use free cutting steel of known quality, but can only get it mail order and at a huge price.I did put the part in the stove overnight and this may have helped. This is a re-accuring problem with me, think it will be best to buy some 1/2″ hss blanks and just keep grinding them up.

[mgjParticipant @mgj]

I dunno Gordon. A lot of the cheapo HSS blanks are not much more than monkey metal.

 

Better to buy a couple of GOOD HSS blanks (ouch because they will cost) and then buy the right steel for the job. Be cheaper in the long run. Good HSS is pretty pricey.

[Paul BoscottParticipant @paulboscott25817]

Gordon

Have you considered mounting your disk in the lathe covering up the slide ways and using the angle grinder bracketed off the tool post to get the part concentric with the lathe so there not any lumps on it to start with? Then treat it like a casting a make the first cut slow and deep enough to get under any local hardening you may have caused

Yours Paul Boscott

[Gordon WParticipant @gordonw]

Thanks to all. I had thought about grinding in the lathe and may do so next time, or make a sort of crude rotary table. I do know about tool grinding etc. but for ind. type work and am new to small model stuff. I think some of the problem is cheapo tools, and esp. HSS. This job now done, it may help someone else to tell what I did;- 1) fitted a leadscrew handle for long. feed, this better than power feed, and much better than using the rack to hand feed. 2) found some very old pieces of 1/2″ sq. Hss ,ground LH & RH tools with minm. relief on all faces and good rad. on point, as suggested. 3) used neat oil to cut. Am fitting big pulley to get a lower speed as my eastern lathe has 120 rpm as the lowest. I had just thought origenally, that there may be some modern stuff that I did not know about, or  some old stuff.

[Nigel McBurney 1Participant @nigelmcburney1]

Hi  The worst of the common materials to machine are steel water pipe then rolled steel plate,they are not really tough but very stringy.forget carbides use good hss with 15 t0 20 degrees rake and SLOW cutting speed ,around 40 to  50 ft per minute using soluble oil or even slower on the first couple of cuts,if as you say your lathes bottom speed is 120 then you are attempting to cut rough steel at at nearly 200 ft a minute which will destroy any tool,your lathe speed should be 25 to 30 rpm.I know there is some low quality hss around,but no hss will last on good steel if you exceed 100 foot a minute surface speed,possibly 120 on soft leaded freecutting material,the tougher the material the lower the speed,thats why carbides were introduced,to enable higher speeds to be used to keep cost down,but they are intended for use on suitable machinery and nice clean known materials under ideal cutting conditions,not rough jobbing engineering .thats why a Myford and my Colchester have low bottom speeds of 25 rpm.Use ordinary soluble oil at 20 to1 mix,The above is not theory I earn my living on jobs like this.

ps dont go using grinding wheels and angle grinders on your lathe. 

[Gordon WParticipant @gordonw]

Thanks for that Nigel, yes I’ve met the tough water pipe as well, but beeing small dia the cutting speeds could be low. New pulley just about ready to fit, should get down to 70 rpm, as low as I can easily get. HSS ,How do I know what I am buying? Prices for 1/2″ sq. x3″ long seem to vary from £2 to £10 ,just assume the dearest is best? For interest the old piece I ground up to do my job is marked Goodyear, I’m assuming it was a form tool for tyre moulds, but maybe not,  good steel anyway

[Ian S CParticipant @iansc]

Hi Nigel,don’t know what water pipe is made of in the UK,I machine water pipe here in NZ as for any mild steel,it cuts ok,I’v used it for cylinders in model hot air engines,the bore comes up nicely.Ian S C

[mgjParticipant @mgj]

Ian I rather agree. Not sure of the spec – just a common or garden low carbon mild, but its often in the drawn state so its work hardened and a bit stringy. If its being a bit feminine, then I just anneal it – like anything else that’s tough (or most else- there are some materials which won’t soften, but they are relatively rare).

 

Mind you, with the right tip you can machine armour plate quite easily and to a good finish, at quite reasonable speed, even in the toughened state. All of these things are just a matter of having ones act togehter.

[Ian S CParticipant @iansc]

Only problem I’v had with water pipe was once when boring it the weld let go.I took it out of the lathe,ground a V down the seam,clamped it up and welded the outside of the seam,put back in lathe,finnish bore.Ian S C

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